Improve usability of init_db script.

* init_db now a hashbang'd script, rather than a .js file.
* init_db tries to chdir to the app root if it thinks it started in scripts/.
   (config complains otherwise)
item_id --> id for all data item types in the schema.

This lines up more nicely with Backbone expectations about JSON
responses -- and while those can be parsed out, it doesn't cause any harm
to improve the fit server-side.
Add date conversion tool to Util, for changing from milliseconds since epoch to
seconds since epoch.
Cleanliness, error handling, id field name change.

* Fixed up error handling to always bubble back up the call stack.
* Added a central error handler for closing out responses and dying/warning.
* Some renaming in libs to differentiate more strongly between libraries and
instances of a model.
* <name>_id --> id, to better fit Backbone's conventions.
Sanity check in app for the db; backgrid in bower.json.
Frontend stuff

* Add support for adding new line items/persisting them.
* Plug in backgrid to show/edit existing ones.
* Remove old templates/views for displaying/editing line items.
* Remove various gitkeep files.
* Remove silly <a> style from style.css, actually load style.css.
* Remove cruft from starter view.
* Some whitespace fixes here and there.
Minor init_db script fix.